Abstract:

In order to obtain higher retention rate of alkyl ketene dimer(AKD) in the slurry system and improve the reaction between AKD and the cellulosic fibers, common of cationic polyacrylamides(CPAM), cationic starch(CS), and bentonite(BN), which are the common retention aids in papermaking systems were chosen to pre-flocculate AKD and thus improved its sizing efficiency. Three AKD pre-flocculation processes(E, F, G) were obtained by changing the addition sequence of the three retention aids. The effects of three pre-flocculate processes on AKD floc particle size, specific surface area, system turbidity, zeta potential, and paper sizing were investigated. The results showed that the pre-flocculation process significantly increased the size of the AKD colloidal particles. The median particle sizes of AKD flocs obtained from processes E, F, and G were 223.144, 310.461 and 263.026 μm, respectively, and the turbidity of the pulp suspension was effectively reduced. Among the three pre-flocculation processes, the pulp-E-PCC, in which the negatively charged bentonite and positively charged CS were attracted with AKD by electrostatic force, followed by the bridging effect from CPAM, generated AKD floc with a stronger binding to fibers. The adsorption of AKD by the fiber reached 2.151 mg/g at 10 min of adsorption. When AKD flocs from process E were blended with PCC for sizing and filling, the Cobb₆₀ value of the paper sheets reduced to 20.15 g/m², filler retention reached 90.51%, and the sizing reversal rate in 40 days decreased to 5.49%.

Key words: sizing, pre-flocculation, AKD, particle size